Epoxy compounds are cured with various curing agents to provide cured products which are excellent in mechanical property, moisture resistance, and electrical properties and are thus used in a wide range of fields such as encapsulation material for electric/electronic parts, molding material, cast material, lamination material, composite material, adhesive, and powdered paint. However, as technology advances, the desire for the high performance of epoxy compound grows. Gradually, the desire can not be satisfied by conventional epoxy compounds. For example, with the development of technology of reducing size and thickness of electrical parts in field of electric/electronic applications, epoxy compound is required to have lower viscosity. This is because the resin must flow to sufficiently reach small spaces in a miniaturized part. As epoxy compounds having low viscosity, diglycidy lether of bisphenol A and diglycidy lether of bisphenol F have been widely used. However, since these epoxy compounds are liquid or viscous at ordinary temperature, the workability should be poor because the difficult handing according to the application. Moreover, cured products from these epoxy compounds are not sufficient in mechanical strength, heat resistance, and moisture resistance.
In order to solve these problems, technologies using epoxy compounds which are crystalline at ordinary temperature and over have been proposed. Examples include tetramethylbiphenyl type epoxy compounds (JP-H07-53791-B) and stilbene type epoxy compounds (JP-H09-12674-A). However, these epoxy compounds have high melt viscosity and insufficient curing property because it has bulky substituents near epoxy groups. Though cured products from these epoxy compounds have heat resistance and moisture resistance somewhat better than those of a cured product from the aforementioned bisphenol A-type epoxy compound, these are still insufficient according to specific applications.
The present invention is intended to provide a novel epoxy compound which is solid at ordinary temperature so as to exhibit excellent handing property and, in its melted state, has extremely low melt viscosity and has excellent curing property and which can provide a cured product which is excellent in mechanical strength, heat resistance, and moisture resistance and a preparation method of the novel epoxy compound and further provide a curable epoxy resin composition containing a novel epoxy compound of the present invention which is useful for applications such as encapsulation material for electric/electronic parts, molding material, cast material, lamination material, composite material, adhesive, and powdered paint, and a cured product thereof.
To encapsulate semiconductor elements, epoxy resin compositions are widely used from the viewpoints of reliability, productivity, and cost. These compositions are required to have flame retardance similar to general plastic materials. For this, besides main components, a combination of brominated epoxy resin such as tetrabromobisphenol A type epoxy resin or brominated phenol novolak epoxy resin and an antimony oxide is added as a flame retardant component.
From environmental standpoint, movement toward restriction in use of compounds containing halogen having possibilities of creating dioxin equivalents and use of toxic antimony compound has been increased. Therefore, as for composition for semiconductor encapsulation, technology for achieving flame retardance without using halogen compound such as a brominated epoxy resin and an antimony oxide mentioned above has been gradually studied. For example, as a method of adding a flame retardant alternative to halogen compound and antimony oxide, a method of adding a red phosphorus (JP-H09-227765-A), a method of adding a phosphoric ester compound (JP-H09-235449-A), a method of adding a phosphazene compound (JP-H08-225714-A), and a method of adding a metal hydroxide (JP-H09-241483-A) have been proposed and a method of increasing the adding rate of filler (JP-H07-82343-A) has been also proposed.
However, the method of adding a red phosphorus to prepare an epoxy resin composition for semiconductor encapsulation has a problem of deterioration in moisture resistance reliability and a safety problem due to impact ignitability of the red phosphorus. The method of adding a phosphoric ester compound and the method of adding a phosphazene compound have a problem of deteriorated moldability due to plasticization and a problem of deterioration in moisture resistance reliability. The method of adding a metal hydroxide and the method of increasing the adding rate of filler have a problem of deteriorated fluidity. Any method hasn't been reached to obtain moldability and reliability equivalent to those of the epoxy resin composition for semiconductor encapsulation using brominated epoxy resin with antimony oxide.
On the other hand, in order to cope with complex mounting configuration, the epoxy resin composition is required to have further improved solder crack resistance. To achieve this, it is necessary to sufficiently take care of fluidity of a composition achieving the increased percentage of filler and low hygroscopicity after cured.
To satisfy these requirements, a technology of satisfying both of fluidity and low hygroscopicity by using a composition composed of a tetramethyl biphenol type epoxy resin having low melt viscosity and a phenol resin such as phenol aralkyl resin having nonpolar substituents (JP-S61-47725-A), a technology of mainly using an epoxy resin made of dicyclopentadiene phenol with the bulky substituents for the purpose of improving hygroscopicity (JP-S61-123618-A) have been proposed. However, none of proposal technologies is environment-friendly. These can not achieve sufficient flame retardance without using halogen compound and antimony compound as a flame retardant.
The present invention is intended to provide an epoxy resin composition for semiconductor encapsulation which exhibits excellent flame retardance without using halogen compound and antimony compound as a flame retardant, further exhibits excellent fluidity because of its low viscosity, and is capable of providing a cured product having superior solder crack resistance because of its low hygroscopicity and to provide a semiconductor device of which semiconductor elements are encapsulated by using the aforementioned epoxy resin composition.